C#：当派生迭代器 class 及其基础实现 IEnumerable 时，在派生迭代器 class 上使用 LINQ

Question

我有一种情况，我有迭代器类我正在推导。基础迭代器迭代基础对象，派生迭代器迭代派生对象。我可以在基本迭代器上使用 LINQ，但不能在派生迭代器上使用。如果我可以使用 LINQ 迭代其中任何一个，那将非常有帮助。

在此先感谢您的指导！

namespace ClassLibrary1
{
    public class BaseThingy { }

    public class DerivedThingy : BaseThingy { }

    public class BaseEnumerator : IReadOnlyCollection<BaseThingy>
    {
        public int Count => throw new NotImplementedException();

        public IEnumerator<BaseThingy> GetEnumerator()
        {
            throw new NotImplementedException();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            throw new NotImplementedException();
        }
    }

    public class DerivedEnumerator : BaseEnumerator, IReadOnlyCollection<DerivedThingy>
    {
        IEnumerator<DerivedThingy> IEnumerable<DerivedThingy>.GetEnumerator()
        {
            throw new NotImplementedException();
        }
    }

    public class Application
    {
        public void Main()
        {
            BaseEnumerator baseEnumerator = new BaseEnumerator();
            DerivedEnumerator derivedEnumerator = new DerivedEnumerator();

            // Works...
            var x = baseEnumerator.Where(s => s.GetHashCode() == s.GetHashCode());

            // Doesn't work...
            var y = derivedEnumerator.Where(s => s.GetHashCode() == s.GetHashCode());
        }
    }
}

Answer 1

那是因为 DerivedEnumerator 同时实现了 IEnumerable<BaseThingy> 和 IEnumerable<DerivedThingy>（通过 IReadOnlyColleciton 间接实现）。所以当你做

var y = derivedEnumerator.Where(s => s.GetHashCode() == s.GetHashCode());

编译器无法确定 lamdba 中 s 的类型。是 DerivedThingy 吗？是 BaseThingy 吗？两者都是可能的。所以你需要明确地告诉它那是什么：

var y = derivedEnumerator.Where<DerivedThingy>(s => s.GetHashCode() == s.GetHashCode());

或

var y = derivedEnumerator.Where((DerivedThingy s) => s.GetHashCode() == s.GetHashCode());

也就是说，这是一个非常不寻常的设计，您可能会重新考虑它。具体如何取决于您要做什么（那么，为什么您需要以这种方式继承枚举器）。

Answer 2

歧义问题

namespace ClassLibrary1
{
    public class BaseThingy { }

    public class DerivedThingy : BaseThingy { }

    public class BaseEnumerator : IReadOnlyCollection<BaseThingy>
    {
        public int Count => throw new NotImplementedException();

        public IEnumerator<BaseThingy> GetEnumerator()
        {
            throw new NotImplementedException();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            throw new NotImplementedException();
        }
    }

    public class DerivedEnumerator : BaseEnumerator, IReadOnlyCollection<DerivedThingy>
    {
        IEnumerator<DerivedThingy> IEnumerable<DerivedThingy>.GetEnumerator()
        {
            throw new NotImplementedException();
        }
    }

    public class Application
    {
        public void Main()
        {
            BaseEnumerator baseEnumerator = new BaseEnumerator();
            DerivedEnumerator derivedEnumerator = new DerivedEnumerator();

            // Works...
            var x = baseEnumerator.Where(s => s.GetHashCode() == s.GetHashCode());

            // Works now
            var y = derivedEnumerator.Where<DerivedThingy>(s => s.GetHashCode() == s.GetHashCode());
        }
    }
}

C#：当派生迭代器 class 及其基础实现 IEnumerable 时，在派生迭代器 class 上使用 LINQ

C#: Using LINQ on a derived iterator class when both the derived class and its base implement IEnumerable

c#

linq

ienumerable

inheritance